Current mobile electronic devices, such as smartphones, tablets and the like, generally have more than one antenna at different locations in the device. One antenna can be selected over another antenna, in an antenna selection (AS) process which is an antenna diversity technique generally used to improve the quality and the reliability of a wireless link. The diversity comes from having the choice to transmit on antennas that experience different near-field environments due, for example, to the presence of the operating user and the close surroundings that each of the antennas sees. The propagation channel characteristics that each antenna interacts with would most likely be different from one antenna to another, adding another factor to diversity as each of the antennas can experience different fading levels for the same usage scenario. In uplink (UL) antenna selection, an uplink signal is fed into one of several available antennas for UL transmission where the antenna selected is based on an optimization criterion.
Even if both antennas are identically designed and offer identical free space (FS) characteristics, both for reception (downlink or DL) and transmission (UL), it is probable that one of the antennas would offer a better long term link performance in practical usage cases due to real-world effects such as hand(s) and/or head placement on the device.